<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>calc()</title>
  <style>
    html,
    body {
      margin: 0;
      padding: 10px;  
      width: 100%;
      height: 100%;
      box-sizing: border-box;
    }
    
    .box {
      width: 100%;
      height: 200px;
      margin: 20px 0;
      border: 1px solid #000;
    }
    .item {
      width: 100px;
      height: 100px;
      background-color:red;
    }
    .item-1 {
      width:calc(100% - 100px);
      height: 100%;
      background-color:bisque;
    }
    .item-2 {
      width:calc(50px + 50px);
      height: 100px;
      background-color:bisque;
    }
    .item-3 {
      width:calc(10px * 10px);
      height: 100px;
      background-color:bisque;
    }
    .item-4 {
      width:calc(1000px / 10);
      height: 100px;
      background-color:bisque;
    }
    .item-5 {
      width:calc(1000px / 10px);
      height: 100px;
      background-color:bisque;
    }
  </style>
</head>

<body>
  <h2>calc(100% - 100px)</h2>
  <div class="box">
    <div class="item-1"></div>
  </div>
  <h2>calc(50px + 50px)</h2>
  <div class="box">
    <div class="item-2"></div>
    <div class="item"></div>
  </div>
  <h2>calc(10px * 10px)</h2>
  <div class="box">
    <div class="item-3"></div>
    <div class="item"></div>
  </div>
  <h2>calc(1000px * 10)</h2>
  <div class="box">
    <div class="item-4"></div>
    <div class="item"></div>
  </div>
  <h2>calc(1000px * 10px)</h2>
  <div class="box">
    <div class="item-5"></div>
    <div class="item"></div>
  </div>
</body>

</html>